URGENT MovieMaker2 Help

I use MM2 all the time with no problems, now I'm trying to save a 52 minute project to a DV-AVI, coming out at 11750MB or thereabouts. An error pops up after it has been saving for a little while and it says "Movie Maker cannot save to the specified location" with a load of other text.

I know that all the source files are on my computer, and that there's about 16GB space for it (about 12GB file)

When i close MM2 after that, it comes up another error - Runtime Error in Visual C++

R6025 -pure virtual function call

Does anyone know what to do because I really need this sorted by Saturday.